This invention relates to a fuel supply control method for internal combustion engines, and more particularly to a method of this kind which is adapted to improve the accelerability of the engine from an idling region thereof.
Fuel supply control methods conventionally employed for controlling the fuel supply to internal combustion engines are generally intended to improve operating characteristics of the engine such as accelerability thereof. Among such fuel supply control methods has been proposed e.g. by Japanese Provisional Patent Publication No. 49-119080 a method which comprises providing a map in which are set a plurality of basic fuel quantity values corresponding, respectively, to a plurality of predetermined combinations of two operating parameters of the engine (e.g. engine rpm and intake pipe absolute pressure), reading from the map a basic fuel quantity value which corresponds to detected values of the two operating parameters, and correcting the read basic fuel quantity value by the use of a correction value corresponding to an operating condition in which the engine is operating, to thereby set a fuel supply quantity optimal to the actual operating condition of the engine.
In such type fuel control method using a basic fuel quantity value map, in order to improve the fuel consumption during idling operation of the engine, some of the basic fuel quantity values of the map that correspond to an idling region of the engine are set at relatively smaller values so as to set the air-fuel ratio of an air-fuel mixture to be supplied to the engine at a leaner value than a theoretical mixture ratio.
However, according to such conventional setting of basic fuel quantity values in the map, if the engine is accelerated with the opening action of the throttle valve when the engine is operating in such idling region, fuel supply control is still continued by the use of basic fuel quantity values set to supply a lean mixture to the engine while the engine is operating in the idling region, even when the engine requires the supply of an increased quantity of fuel required for such acceleration. As a consequence, a rich mixture is not supplied to the engine until after the engine has left the idling region, resulting in deterioration of the accelerability of the engine. The above map setting of basic fuel quantity values is also disadvantageous when applied to a control method of starting to control the air-fuel ratio of the mixture to a predetermined or stoichiometric value upon opening of the throttle valve, in that it is difficult to promptly control the air-fuel ratio to the above predetermined or stoichiometric value upon a transition from the idling region to the feedback control region. Furthermore, the above map setting has difficulties in applying same to a control method of varying the fuel supply quantity to the engine in response to on-off actions of auxiliary equipments of the engine as well, in that to obtain a predetermined increased fuel supply quantity corresponding to an on state of an auxiliary equipment, two different correction values as aforementioned have to be provided for increasing the basic fuel quantity value between the idling region and the feedback control region, inviting complexity of the fuel supply control.
The same problems as above are also encountered in the fuel supply control of internal combustion engines equipped with auxiliary chambers.